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Generator TypesReciprocating Internal Combustion Engine and Generator SetReciprocating engines are the most common technology in use today among electrical generator applications. The typical unit is fueled with either diesel or natural gas. Numerous manufacturers make engine-generator sets in a wide range of horsepower, RPM, and kW output. Natural gas units are preferred because of fuel access (these can be easily connected to a building�s existing gas service) and because emissions are cleaner than diesel. The electric efficiency of these generators is between 18% and 38% (fuel energy in verse electric energy out). Higher system efficiencies are achieved by using the waste heat a space or to heat hot water. The purchase price of a gas fired generator (natural gas or propane) is typically in the $350 - $430 /kW range (smaller units cost more per kW than larger units). Operating costs are between $.03 and $.07 per kWh depending on gas costs ($3 to $4 per mcf of gas) and efficiency of the engine. Maintenance and warrantee costs are between $.005 and $.007 per kWh. Reciprocating engine generators are the most reliable and cost effective of the smaller generating units. There are more of these diesel and natural gas engine generating units in place, consequently maintenance and service is easier to find and less expensive than other electric generation technologies. Micro-Turbine Generator SetMicro-turbines are a third generation evolution from many civil and military aviation and maritime applications. Based on the gas turbine engine developed in 1938 in England, a micro-turbine utilizes very high internal combustion pressures to rotate a power output shaft. Rotation and torque of a power output shaft is transferred, in the case of a micro-turbine generator, to an alternating current electrical generator. Typically a turbine contains only a few moving parts, making it simple, in theory, to maintain. Micro-turbines have efficiencies that range from 21% to 31%. Higher system efficiencies are possible by utilizing the waste heat generated from the exhaust gases. Micro-turbines require natural gas at high pressure (75psi) which may mean an on-site compressor that adds cost and reduces the system efficiencies. Micro-turbines range in size from 25 kW to 1,000 kW. The micro-turbine is a modular design, which allows numerous units to be combined to develop multiples of electrical kW output. Typical equipment cost is $ 375 to $450 per kW, however getting one, at any price, seems to be very difficult. Apparently many companies have pushed to begin production however, due to problems, they are not able to deliver them. Our concern in using micro-turbines is due to the lack of experience in the marketplace. Noise and safety are two additional issues with micro-turbines. Anything with parts that turn at 18,000 RPM should give one cause for concern. Fuel CellsFuel cells are an environmentally clean, quiet, and highly efficient method for generating electricity and heat from natural gas and other fuels. Fuel cells are an ideal technology for small power plants since their very clean emissions and almost silent operation allow them to be sited in cities- next to buildings and homes- near electric loads. A fuel cell is similar to a battery in many ways. Both use an electro-chemical process to convert chemical energy into electric power. But a fuel cell is different in one very important way: It never runs down as long as fuel is supplied to the cell. Hydrogen (from natural gas or gasoline) is the fuel which powers a fuel cell. In its simplest form, a fuel cell power system consists of a fuel processor (to extract hydrogen), a power cell, and a power conditioner (to get 60 Hz AC power). Typical fuel cells have electric efficiencies starting at 40% making them very efficient. When by-product heat is utilized, system efficiency can approach 80%. The cost of fuel cells is very high, between $2,800 and $3,500 per kW. For this reason, fuel cells are not a viable option in most instances. There are fuel cells in operation, but they are primarily limited to test sites which have been subsidized by various government and business interests. As with other technologies a side benefit of the electrical energy produced is waste heat is generated that can be used for production of domestic or process hot water, or for space heating purposes. |
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